I am having this problem too. At first, I thought it was because I was running an app while the messages were supposed to come in, but it just seems to not get them every once in a while. This is actually a replacement because the at&t people thought the first phone just had a bug or something. Then I called at&t about it and they said they were going to have me "switch towers" or something like that. After, it seemed like everything was fine. But a few days later, it started happening again. I just test it by doing the airplane mode fix that someone posted above. Also, I don't seem to get phone calls during this down time as well. Anyone know what the problem is?